The present invention relates generally to internal combustion engines and more specifically to an apparatus for recognizing spark knock during the operation of the engine.
Spark knock is the phenomenon that occurs when a combustion flame in a cylinder of an engine propagates near the speed of sound. If knock is left uncontrolled, engine damage may occur and emissions levels may increase. Many engine control strategies have developed to remedy spark knock. For example, retarding the ignition point and making the air fuel mixture richer are both strategies employed to reduce spark knock.
Accurate detection of spark knock is essential to the durability of an internal combustion engine. Previously, there have been several attempts at accurately determining spark knock. Commonly, systems for determining spark knock use a peak detection-type configuration which compares a vibration signal from an engine sensor to a predetermined threshold. However, such systems have proved unreliable due to increased mechanical and electrical noise in the engine compartment especially at high engine speeds. Increased mechanical and electrical noise decreases the signal-to-noise ratio, making accurate detection difficult. Such systems also have proven to be unreliable in the long term because the threshold values are determined for new engines. Prior art thresholds do not compensate for aging of an engine, causing a generally decreasing detection during the life cycle of the engine.
One method of spark knock detection using a threshold is disclosed in U.S. Pat. No. 5,201,292. The '292 patent describes a spark knock detection system which breaks the signal up into energy components and spectral components. Each portion is compared to predetermined thresholds. If the energy component signal or spectral component exceeds its corresponding threshold then there is knock. However, even if the thresholds are adaptively predetermined, the system may very well give errors based on the system noise particularly when the vehicle is running at high RPM. In other words, if the noise peak rises above a predetermined threshold then a knock signal is detected. Another source of error in such a system is if a rock hits the oil pan or other engine component. The noise produced may be determined as a spark knock. Such a system is believed detect an undesirable number of errors.
It would therefore be desirable provide a system with a having a high accuracy rate at all portions of the life cycle of an engine.